The invention relates to marine drive exhaust systems, and more particularly to exhaust manifolds and elbows.
In a marine propulsion system, an internal combustion engine is exhausted through a water jacketed exhaust manifold and a water jacketed exhaust elbow. Engine exhaust is directed through the manifold and into the elbow and around a bend in the elbow to a discharge exhaust passage. The exhaust passages are surrounded by water passages for cooling the engine exhaust. The water mixes with the exhaust at the end of the discharge exhaust passage. Examples of prior exhaust systems are shown in U.S. Pat. Nos. 3,541,786, 4,573,318, 4,711,088, 4,866,934, and 4,977,741, incorporated herein by reference.
In one aspect of the present invention, an exhaust assembly is provided combining the manifold and elbow, and having exhaust divider runner walls extending from the manifold portion into the elbow portion and at least partially around the elbow bend and defining and separating intake exhaust passages in the manifold portion into individual passages merging into individual respective transfer exhaust passages in the elbow portion, and defining and separating the transfer exhaust passages into individual passages merging into a common passage at the discharge exhaust passage downstream of the elbow bend. The exhaust divider structure provides a smooth continuous transition of exhaust gas flow from the intake exhaust passages to the transfer exhaust passages to the discharge exhaust passage, and minimizes turbulent flow of exhaust through the manifold portion and the elbow portion. The exhaust divider runner wall structure has been found to increase horsepower.
In another aspect of the invention, steam build-up in the water jacket is prevented by providing an upper vent at the high point of the elbow bend, and a lower vent below the discharge exhaust passage. The upper vent is provided by a steam outlet opening in the water jacket at the high point of the elbow bend, and a steam exhaust channel formed along the exterior of the water jacket .nd extending from the steam outlet opening to direct steam to the end of the discharge exhaust passage to mix with water and exhaust thereat. The lower vent may also supply cooling water to an unjacketed section of the discharge exhaust passage along the underside thereof to cool same when water is flowing through the water jacket.
In another aspect of the invention, each transfer exhaust passage extending from its respective intake exhaust passage has its own water supply inlet adjacent a respective exhaust inlet opening in the manifold portion and at the upstream end of the respective intake exhaust passage. The water inlet openings are provided by cast fittings each extending along an axis offset from and generally parallel to the axis of engine exhaust flow into the exhaust inlet opening and in the opposite direction thereto.
In another aspect of the invention, a plurality of wall supports are provided between the water jacket and the elbow portion, which wall supports are angled to deflect and direct water flow upwardly to the top of the elbow portion.
In another aspect, the invention enables the manifold portion, elbow portion, and water jacket portion to be integrally lost foam cast from stainless steel as a unitary one piece member, including the noted exhaust divider runner walls, steam exhaust channel, and wall supports. The wall supports prevent collapsing of the water jacket portion and elbow portion toward each other during lost foam casting of the stainless steel material. The cast stainless steel exhaust assembly eliminates problems encountered with prior manifolds and elbows of cast iron or ductile iron, which are subject to rusting, primarily where the manifold is mounted to the engine. The extremely high temperature in such area burns paint away, and the exposure to water creates rust. The present invention enables the exhaust assembly to be formed of stainless steel, which provides improved corrosion resistance. The invention also enables lost foam casting of the exhaust assembly, which eliminates slag from forming and blocking water passages, which can be a problem in prior cast iron and ductile iron assemblies. The invention further enables thin wall construction, and an accompanying reduction in size and weight. The noted wall supports prevent collapse of such thin wall construction. The wall supports include a plurality of staggered spaced parallel segments in louver arrangement providing the noted angle to deflect and direct water flow therebetween upwardly to the top of the elbow portion and around the bend.
In another aspect, the invention enables the exhaust assembly to extend outwardly from a first engine surface having exhaust ports and curving and extending past a valve cover on a second adjacent engine surface, and spaced from the valve cover a sufficient distance to enable clearance and removal of the valve cover past the exhaust assembly without requiring disassembly or removal of the exhaust assembly.
In another aspect of the invention, the exhaust discharge passage extends downwardly at a 13.degree. angle relative to horizontal, to match the standard boat transom angle. This in turn enables the exhaust from the discharge end of the elbow portion to flow straight through the transom at a 90.degree. angle relative thereto, without further bends or deflections in the coupling hose or pipe structure between the end of the elbow portion and the transom.